This bit of good news came from HTC Product Manager Leigh Momii's Twitter account. According to her, the update will be coming from Verizon this week. The HTC web page monitoring the progress and roll out of Sense 6 still marks the Verizon variant as under the Certification stage, as switching it over to Completed would formally signal the start of the rollout.
As with other Sense 6 updates, this will bring the One M7 closer to feature parity with the One M8. Of course, it is still limited by difference in hardware, but they will be the same in some things that matter most, like the new Blinkfeed, Zoe, and perhaps some of the Motion Launch gestures. One should not expect to see the camera effects that require a Duo Camera setup that the older One doesn't have.
There is still no specific date when the update will start, but hopefully no major release blockers happen before this week is over. Neither HTC nor Verizon are saying how large the update will be, but it is always a good idea to be prepared with backups, battery, and a stable WiFi connection for major changes such as these.
SOURCE: @Leigh Momii